Method and polishing pad design enabling improved wafer removal from a polishing pad in a CMP process

ABSTRACT

The invention provides a chemical mechanical polishing pad and method that enables improved wafer removal from the polishing pad after completion of chemical mechanical polishing of the wafer.

PRIORITY REFERENCE TO PRIOR APPLICATIONS

[0001] This application claims benefit of and incorporates by referenceU.S. patent application serial No. 60/430,947, entitled “Method AndPolishing Pad Design Enabling Improved Wafer Removal From The PolishingPad In A CMP Process,” filed on Dec. 4, 2002, by inventors AlejandroReyes, Gerard Moloney, Cormac Walsh, and Ernesto Saldana.

TECHNICAL FIELD

[0002] This invention relates generally to chemical mechanical polishing(CMP), and more particularly, but not exclusively, provides a CMPpolishing pad and method for improving the removal of a wafer from apolishing pad after CMP.

BACKGROUND

[0003] CMP is a combination of chemical reaction and mechanical buffing.A conventional CMP system includes a polishing head with a retainingring that holds and rotates a substrate (also referred tointerchangeably as a wafer) against a polishing pad surface rotating inthe same direction. The polishing pad can be made of cast and slicedpolyurethane (or other polymers) with a filler or a urethane coatedfelt.

[0004] During rotation of the substrate against the polishing pad, aslurry of silica (and/or other abrasives) suspended in a mild etchant,such as potassium or ammonium hydroxide, is dispensed onto the polishingpad. The combination of chemical reaction from the slurry and mechanicalbuffing from the polishing pad removes vertical inconsistencies on thesurface of the substrate, thereby forming an extremely flat surface.

[0005] In order to reduce operating costs and human intervention intothe CMP system there has been a push to use CMP consumables with alonger operating life. An example of one of these consumables is what isreferred to within the industry is a perforated polishing pad. Anexample of a perforated polishing pad is a polishing pad 130 a as shownin FIG. 1 and FIG. 2 (not to scale). The polishing pad 130 a has aplurality of holes or perforations 170 spread uniformly over the surfaceof the polishing pad 130 a. The perforations 170 act to distributeslurry locally during CMP when the polishing pad 130 a is compressed.

[0006] However, one of the drawbacks of the perforated pad 130 a is thedifficulty of lifting a wafer from the pad after polishing. The holes170 in the pad 130 a act as suction cups and the vacuum force appliedthrough the polishing head to the back side of the wafer can not easilyovercome this suction force between the front side of the wafer and thepad.

[0007] For example, FIG. 1 shows a conventional CMP system 100 a with aperforated polishing pad 130 a. The polishing pad 130 a rests on aplaten 140 on a turn table 150. The polishing head 180 includes acarrier 120 and a retaining ring 110 that retains a wafer 160 during CMPand can also include other components not shown. After CMP is complete,a vacuum force is applied to a backside of the wafer 160 (i.e., the sideof the wafer 160 facing the carrier 120) and the polishing head 180lifts the wafer 160 off of the polishing pad 130 a.

[0008] Applying the vacuum to the backside of the wafer 160 causes thewafer 160 to bow since the edge of the wafer is sealed against the padat points 165. This bowing of the wafer 160 causes a secondary vacuumforce between the pad 130 a and the wafer 160 thereby making it moredifficult for the polishing head 180 to lift the wafer 160.

[0009] One solution to this deficiency to improve the ease of removingthe wafer 160 from the polishing head 180 after CMP includes moving thepolishing head 180 and wafer 160 over the edge of the polishing pad 130a to relieve the vacuum force between the polishing pad 130 a and thewafer 160. However, this can lead to increased wafer defects andscratches as the edge of the polishing pad 130 a entraps polishingdebris that can damage the wafer 160. Further, moving the wafer 160 tothe edge of the polishing pad 130 a can lead to breakage of the wafer160 since this leads to uneven stress distribution on the wafer 160 as aportion of the wafer is overhanging the polishing pad 130 a prior toliftoff.

[0010] Therefore, a new polishing pad and method are needed thatovercome the above-mentioned shortcomings while substantially decreasingthe chance of wafer damage.

SUMMARY

[0011] Embodiment of the invention provides a chemical mechanicalpolishing pad and method of using the same to ease removal of a waferfrom the pad after completion of CMP. The pad includes a top surface andat least one venting inlet. The top surface has a structure that forms avacuum between the pad and a wafer during chemical mechanical polishing.The at least one venting inlet releases the vacuum when the wafer islocated over the venting inlet. In one embodiment of the invention, thestructure includes perforations. In another embodiment, the structureincludes grooves.

[0012] An embodiment of the method starts with the applying of a vacuumto a backside of the wafer. After applying the vacuum, a polishing headretaining the wafer is moved to a periphery of the polishing pad. Thepolishing pad is then rotated so that at least one venting inlet passesunderneath the wafer, thereby releasing the vacuum between the pad andthe wafer. The vacuum on the backside of the wafer is then released andwafer removed from the polishing head.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Non-limiting and non-exhaustive embodiments of the presentinvention are described with reference to the following figures, whereinlike reference numerals refer to like parts throughout the various viewsunless otherwise specified.

[0014]FIG. 1 is a diagram illustrating a conventional CMP system;

[0015]FIG. 2 is a diagram illustrating a conventional perforatedpolishing pad;

[0016]FIG. 3 is a diagram illustrating a perforated polishing padaccording to an embodiment of the invention;

[0017]FIG. 4A-FIG. 4E are diagrams illustrating cross-sections ofpolishing pads according to different embodiments of the invention;

[0018]FIG. 5 is a diagram illustrating a CMP system using the perforatedpolishing pad of FIG. 3; and

[0019]FIG. 6 is a flowchart illustrating a method of CMP using theperforated polishing pad of FIG. 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0020] The following description is provided to enable any person ofordinary skill in the art to make and use the invention, and is providedin the context of a particular application and its requirements. Variousmodifications to the embodiments will be readily apparent to thoseskilled in the art, and the principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Thus, the present invention is not intended tobe limited to the embodiments shown, but is to be accorded the widestscope consistent with the principles, features and teachings disclosedherein.

[0021]FIG. 3 is a diagram illustrating a perforated polishing pad 130 baccording to an embodiment of the invention. The polishing pad 130 b iscircular in shape with a thickness between about 50 and about 80 mils.The polishing pad 130 b can comprise a plurality of planar layers. Thediameter of the polishing pad 130 b can range from about 66 centimetersto about 81 centimeters. The polishing pad 130 b can be made of cast andsliced polyurethane (or other polymers) with a filler or a urethanecoated felt. It will be appreciated by one of ordinary skill in the artthat the polishing pad 130 b can have a thickness or diameter greaterthan or smaller than the thickness and diameter ranges described above.Further, the polishing pad 130 b can also be made of other materialsthan described above.

[0022] The polishing pad 130 b includes a plurality of perforations 170spread uniformly across a planar top and a planar bottom surface of thepolishing pad 130 b. In an alternative embodiment, the polishing pad 130b may include grooves in place of or in addition to the perforations 170in the top surface of the polishing pad 130 b. In another embodiment ofthe invention, the polishing pad 130 b can include any structures thattend to form a vacuum force between the wafer 160 and the polishing pad130 b.

[0023] The polishing pad 130 b also includes four angled venting inlets300 that are distributed along on the periphery of the polishing pad 130b and extend inwards from the edge of the polishing pad 130 b towardsthe center of the polishing pad 130 b. The venting inlets 300 can beevenly or unevenly distributed along the top surface of the polishingpad 130 b.

[0024] Each venting inlet 300 includes a mouth 310 at the periphery ofthe polishing pad 130 b and a terminus 320 at an interior end of theventing inlet 300 thereby forming an axial length there between. Theaxial length of the venting inlets 300 should not extend any fartherthan necessary to ensure venting of the vacuum between the polishing pad130 b and the wafer 160 after CMP and so that the venting inlets 300 donot extend underneath the wafer 160 during CMP as that could lead to anuneven wafer removal profile. The terminus 320 can comprise any shapedending, including an oval ending, a flat ending, a circular ending, aspherical ending, etc.

[0025] The venting inlets 300 can have a width of about 5 to about 10 mmwith a length of about 20 mm. The width of the venting inlets 300 arepreferably minimized to limit wafer 160 deflection but large enough sothat residual water or other fluids from the CMP process do not helpmaintain a seal and stop the vacuum from venting though the ventinginlets 300. The venting inlets 300 can travel through the full thicknessof the polishing pad 130 b or only travel through a portion (e.g., 10mils) of the full thickness (e.g., 50 mils) of the polishing pad 130 b.The venting inlets 300 are angled along the top surface of the polishingpad 130 b at about 45 degrees from the edge of the polishing pad 130 b.The venting inlets 300 are angled so as to increase water and/or otherfluid removal from the venting inlets via centrifugal force. It will beappreciated by one of ordinary skill in the art that the venting inlets300 can also be straight (i.e., perpendicular to the edge of thepolishing pad 130 b) or be angled at other than 45 degrees from the edgeof the polishing pad 130 b. In addition, it will be appreciated that thepolishing pad 130 b can have fewer (i.e., 1) or additional ventinginlets 300. For example, in one embodiment of the invention, thepolishing pad 130 b has 24 venting inlets 300.

[0026]FIG. 4A-FIG. 4E are diagrams illustrating cross-sections ofpolishing pads 130 b according to different embodiments of theinvention. In one embodiment shown in FIG. 4A, a polishing pad 130 b.1has at least one venting inlet 300.1 that extends inwards from a mouth310.1 at the periphery of the polishing pad 130 b.1 to a terminus 320.1at an inner end of the venting inlet 300.1. The venting inlet 300.1 isplanar and parallel to a top surface and a bottom surface of thepolishing pad 130 b.1. Further, the venting inlet 300.1 only extendsthrough a portion of the thickness of the polishing pad 130 b.1,specifically, from the top surface of the polishing pad 130 b.1 to adepth of, for example, about 20 mils in a polishing pad having athickness of 50 mils.

[0027]FIG. 4B illustrates a cross-section of another polishing pad 130b.2 that has at least one venting inlet 300.2 that extends inwards froma mouth 310.2 at the periphery of the polishing pad 130 b.2 to aterminus 320.2 at an inner end of the venting inlet 300.2. The ventinginlet 300.2 only extends through a portion of the thickness of thepolishing pad 130 b.2, specifically, from the top surface of thepolishing pad 130 b.2 to a sloped surface 400 having a first depth atthe terminus 320.2 and second depth, which is greater than the firstdepth, at the mouth 310.2. For example, the first depth can be about 20mils and the second depth can be about 30 mils. The sloped surface 400enables increased water or other fluid removal from the venting inlet130 b.2 due to gravity.

[0028]FIG. 4C illustrates a cross-section of another polishing pad 130b.3 that has at least one venting inlet 300.3 that extends inwards froma mouth 310.3 at the periphery of the polishing pad 130 b.3 to aterminus 320.3 at an inner end of the venting inlet 300.3. The ventinginlet 300.3 extends through the full depth of the polishing pad 130 b.3.

[0029]FIG. 4D illustrates a cross-section of another polishing pad 130b.4 that has at least one venting inlet 300.4 that tunnels inwards andunder the pad 130 b.4 from a mouth 310.4 at the periphery of thepolishing pad 130 b.4 to a terminus 320.4 on a top surface of thepolishing pad 130 b.4 at an inner end of the venting inlet 300.4. Theventing inlet 300.4 uses a top surface of the platen 140 as a bottomsurface of the venting inlet 300.4.

[0030]FIG. 4E illustrates a cross-section of another polishing pad 130b.5 that has at least one venting inlet 300.5 that tunnels inwards andupwards from a mouth 310.5 at the periphery of the polishing pad 130 b.5to a terminus 320.5 on a top surface of the polishing pad 130 b.5 at aninner end of the venting inlet 300.5. The sloped surface of the ventinginlet 300.5 increases the rate of water or other fluid removal from thepad 130 b.5 due to gravity. Alternatively, the venting inlet 300.5 caninclude a flat surface.

[0031]FIG. 5 is a diagram illustrating a CMP system 100 b capable ofusing the perforated polishing pad 130 b (i.e., any of 130 b.1 to 130b.5). The polishing pad 130 b rests on a platen 140 on a turn table 150.The polishing head 180 includes a carrier 120 and a retaining ring 110that retains a wafer 160 during CMP and can include other components notshown. After CMP is complete, a vacuum force is applied to a backside ofthe wafer 160 and the polishing head 180 moves the wafer 160 towards theperiphery of the polishing pad 130 b so that the wafer 160 overhangs aventing inlet 130 (but does not overhang the periphery of the polishingpad 130 b).

[0032] The venting inlet 300 enables the venting of air between thepolishing pad 130 b and the wafer 160, thereby releasing any vacuumforces between the polishing pad 130 b and the wafer 160. Accordingly,the polishing head 180 can then pick up the wafer 160 without the riskof damage to the wafer 160 that is associated with conventionalpolishing pads.

[0033] In an embodiment in which the polishing pad 130 b has only asingle venting inlet 300, the polishing head 180 must move the wafer 160to the periphery of the polishing pad 130 b having the venting inlet300. Alternatively, the polishing pad 130 b can be rotated so that theventing inlet 300 passes beneath the wafer 160. However, in anembodiment in which the polishing pad 130 b has a plurality of ventinginlets 300, the polishing head 180 need only move the wafer 160 to theperiphery of the polishing pad 130 b to ensure that the wafer 160overlaps one or more venting inlets 300. Accordingly, there is no needto move the wafer to a specific section of the periphery of polishingpad 130 b or to rotate the polishing pad 130 b.

[0034]FIG. 6 is a flowchart illustrating a method 600 of CMP using theperforated polishing pad 130 b. First, chemical mechanical polishing iscompleted (610) using the polishing pad 130 b. Next, a vacuum is applied(620) to the backside of the wafer 160. The polishing head 180 and wafer160 are then moved (630) to the periphery of the polishing pad 130 b. Inanother embodiment of the invention, the moving (630) can take placebefore the applying (620).

[0035] If necessary, the polishing pad 130 b is then rotated (640) sothat at least one venting inlet 300 passes underneath the wafer 160 soas to release any vacuum formed between the wafer 160 and the polishingpad 130 b. If the polishing pad 130 b has a plurality of venting inlets300, then rotation (640) may not be needed since moving (630) the head180 and wafer 160 to the periphery of the polishing pad 130 b issufficient for passing the wafer 160 over a venting inlet 300.

[0036] After rotating (640) or moving (630), the polishing head 180 andwafer 160 are lifted (650) from the polishing pad 130 b. As the vacuumbetween the wafer 160 and the polishing pad 130 b has been released, thepolishing head 180 and wafer 160 are relatively easily lifted from thepolishing pad 130 b, thereby limiting the stress on the wafer 160. Thepolishing head 180 is then moved (660) to a wafer unload position and avacuum is released (670) from the backside of the wafer 160. The wafer160 is then removed (680) from the polishing head 180. The method 600then ends.

[0037] The foregoing description of the illustrated embodiments of thepresent invention is by way of example only, and other variations andmodifications of the above-described embodiments and methods arepossible in light of the foregoing teaching. For example, the ventinginlets 300 can be perpendicular or angled with respect to the edge ofthe polishing pad 130 b. The embodiments described herein are notintended to be exhaustive or limiting. The present invention is limitedonly by the following claims.

What is claimed is:
 1. A chemical mechanical polishing pad, comprising:a top surface having a structure that forms a vacuum between the pad anda wafer during chemical mechanical polishing; and at least one ventinginlet capable of releasing the vacuum when the wafer is located over theventing inlet.
 2. The pad of claim 1, wherein the structure includes aplurality of perforations.
 3. The pad of claim 1, wherein the structureincludes a plurality of grooves.
 4. The pad of claim 1, wherein the atleast one venting inlet is connected to atmospheric pressure.
 5. The padof claim 1, wherein the at least one venting inlet extends from theperiphery of the top surface towards the center of the top surface. 6.The pad of claim 1, wherein the at least one venting inlet is angledrelative to a diameter of the pad.
 7. The pad of claim 1, wherein the atleast one venting inlet passes through the full depth of the polishingpad.
 8. The pad of claim 1, wherein the at least one venting inletpasses through a portion of the depth of the polishing pad.
 9. The padof claim 1, wherein the at least one venting inlet has a sloped surface.10. The pad of claim 1, wherein the at least one venting inlet tunnelsthrough the pad to connect with the top surface of the pad.
 11. The padof claim 1, wherein the at least one venting inlet tunnels underneaththe pad to connect with the top surface of the pad and wherein a platenforms a bottom surface of the at least one venting inlet.
 12. A methodfor removing a wafer from a polishing head after chemical mechanicalpolishing, comprising: applying a vacuum to a backside of the wafer;moving the polishing head retaining the wafer so that the wafer ispositioned over a venting inlet of a polishing pad; releasing the vacuumfrom the backside of the wafer; and removing the wafer from thepolishing head.
 13. The method of claim 12, wherein the polishing padhas a top surface having a plurality of perforations.
 14. The method ofclaim 12, wherein the polishing pad has a top surface having a pluralityof grooves.
 15. The method of claim 12, wherein the venting inlet isconnected to atmospheric pressure.
 16. The method of claim 12, whereinthe venting inlet extends from the periphery of a top surface of the padtowards a center of the top surface.
 17. The method of claim 12, whereinthe venting inlet is angled relative to a diameter of the pad.
 18. Themethod of claim 12, wherein the venting inlet passes through the fulldepth of the polishing pad.
 19. The method of claim 12, wherein theventing inlet passes through a portion of the depth of the polishingpad.
 20. The method of claim 12, wherein the venting inlet has a slopedsurface.
 21. The method of claim 12, wherein the venting inlet tunnelsthrough the pad to connect with a top surface of the pad.
 22. The methodof claim 12, wherein the venting inlet tunnels underneath the pad toconnect with a top surface of the pad and wherein a platen forms abottom surface of the venting inlet.
 23. The method of claim 12, whereinthe method is performed in the order recited.
 24. The method of claim12, wherein the moving is performed before the applying.
 25. A methodfor removing a wafer from a polishing head after chemical mechanicalpolishing, comprising: applying a vacuum to a backside of the wafer;moving the polishing head retaining the wafer to a periphery of apolishing pad; rotating the polishing pad so that a venting inlet of thepolishing pad is positioned under the wafer; releasing the vacuum fromthe backside of the wafer; and removing the wafer from the polishinghead.
 26. The method of claim 25, wherein the polishing pad has a topsurface having a plurality of perforations.
 27. The method of claim 25,wherein the polishing pad has a top surface having a plurality ofgrooves.
 28. The method of claim 25, wherein the venting inlet isconnected to atmospheric pressure.
 29. The method of claim 25, whereinthe venting inlet extends from the periphery of a top surface of the padtowards a center of the top surface.
 30. The method of claim 25, whereinthe venting inlet is angled relative to a diameter of the pad.
 31. Themethod of claim 25, wherein the venting inlet passes through the fulldepth of the polishing pad.
 32. The method of claim 25, wherein theventing inlet passes through a portion of the depth of the polishingpad.
 33. The method of claim 25, wherein the venting inlet has a slopedsurface.
 34. The method of claim 25, wherein the venting inlet tunnelsthrough the pad to connect with a top surface of the pad.
 35. The methodof claim 25, wherein the venting inlet tunnels underneath the pad toconnect with a top surface of the pad and wherein a platen forms abottom surface of the venting inlet.
 36. The method of claim 25, whereinthe method is performed in the order recited.
 37. The method of claim25, wherein the moving is performed before the applying.